Subwoofer Selection Criteria

[Ultrasonic]

«Overall distortion limits based on all the frequencies and levels surveyed resulted in the re- quirement that the second harmonic be less than 3%, the third harmonic be less than 1%, and the higher harmonics be less than 0.3-0.1%».

Ask your dealer if he can deliver something on these criteria...

I am not an optimist, 30 years later.

May I ask over what frequency range you/the paper had in mind with those requirements? Is it the full 12-32 Hz in the abstract? I have only made nearfield measurements of my own relatively modest sub (BK Monolith) down to 30 Hz but here it easily exceeds these requirements. I strongly suspect more modern DSP assisted subs from the likes of PSA, JL Audio, Rythmik etc will exceed these requirements over a considerable frequency range. Importantly for the main thrust of this discussion I'd be pretty confident that whatever they do achieve it will exceed the distortion performance of traditional floorstanding speakers.

Here's distortion data for a nearfield measurement for my BK Monolith (with the numbers in the legend being for the cursor position of 30 Hz):

(I'll make a measurement down to lower frequencies when I get chance, and obviously I do expect the performance to get worse there.)

 

[audioBliss]

The most important part of choosing a subwoofer is that you need AT LEAST two of them(and in that case some very powerful ported 12"+ or sealed 18"). I ended up building six sealed 12" subs. You really want to offload the rest of your speakers to lower distortion from them or else there is no point. You also don't want distortion in the bass even though we are less sensitive to it..and you need a lot of capacity in the bass to have low distortion. I see too many people with one lonely sub in the corner that's basically not even more powerful than the front speakers just so that they have a sub...

I cannot stress enough that you basically can't get enough headroom in the bass region. You want as much headroom as possible..and as even as possible. I started with two 10", then when to four 10" with longer throw and now I run six 12". It's not until this last upgrade I'm starting to get that relaxed, even bass that comes naturally and doesn't feel forced. The fewer subs I've owned the more bloated and bassy the sound has been. My room is 3.86 x 6.32 x 2.20 meters just to give some reference.

If you're a bit handy I really recommend that you find a driver that you like then build your own cabinets. There is a ton of info online.

Right now I have stacked three on top of each other at the midpoint in the front and three side by side behind the couch. Having a few subs close by really increases the tactile feel.

With some more careful placement and room treatment my dips should disappear..until I rebuild my room this is way more than good enough. I boost at most 2dB with Dirac so all that below 20Hz is just crazy room gain. Doesn't sound unbalanced actually since you need such insane levels down there to actually feel the bass.

 

[pozz]

Ideally, a sub would have two sealed servo-controlled woofers in dipole configuration.

And as soon as I get the money for two such beasts I would try David Griesinger's placement advice for optimal (psychoacoustic) envelopment, the idea being there that bass should be perceived as if it's coming from all around instead of centered and "in the head".

 

[GrimSurfer]

Some excellent points raised by folks here. To recap/pile on:

1. Match the size of the sub to the room. Too much sub in too small a space will sound terrible.

2. When you think you've found the right sub, buy two of them. It's not about adding bass/power, it's about placing two subs asymmetrically in a room to even out nodes.

3. Room correction software can be overwhelmed. It has much better odds of finding the sweet spot if you first do all of the old school stuff (graph and calculate cut-offs, do a sub crawl, and match levels) before employing it.

4. Subs shouldn't be heard or even felt. A sub is meant to cover, but not accentuate, the low frequencies that all bookshelf and most floor standing speakers cannot reproduce without dropping off SPL.

 

[Ultrasonic]

1. Match the size of the sub to the room. Too much sub in too small a space will sound terrible.

I don't see how. It might end up being a waste of money in terms of unecessary headroom but there is no reason for a big/powerful sub to sound worse.

 

[Ultrasonic]

@audioBliss do you have any measured comparative distortion data for your different setups that you'd be prepared to share?

 

[andreasmaaan]

it's about placing two subs asymmetrically in a room to even out nodes.

You mean symmetrically, right?

 

[Ultrasonic]

You mean symmetrically, right?

Not wanting to speak for GrimSurfer but no, there are very good reasons for having subs in different positions, like one in a corner and a second at the mid-point of a wall. Even better is to have subs at different heights as well but this is less practical for most.

 

[GrimSurfer]

You mean symmetrically, right?

Nope. Asymmetrically.

 

[andreasmaaan]

Nope. Asymmetrically.

Which school(s) of thought are you following here? Or if your own ideas, could you please explain your reasoning?

 

[GrimSurfer]

I don't see how. It might end up being a waste of money in terms of unecessary headroom but there is no reason for a big/powerful sub to sound worse.

Think about a dorm room. How are you going to get that SB 16 Ultra to ever sound right if it is less than four feet from your ear (and before you say no dorm room is that small, think about sub placement from the back wall)?

This is an extreme example but just as you need to select the right mains to rooms to get proper sound, you have to do the same with subs.

And you are absolutely correct wrt wasting money.

 

[Ultrasonic]

For anyone curious, the Room Simulator in Room EQ Wizard is a good way to get an idea of the effects of different combinations of sub positions.

 

[svart-hvitt]

Which school(s) of thought are you following here? Or if your own ideas, could you please explain your reasoning?

I think Geddes argues along these lines. In a «statistical» sense, where should you put your subwoofers to have them contributong to overall sound as independently as possible?

 

[Ultrasonic]

Think about a dorm room. How are you going to get that SB 16 Ultra to ever sound right if it is less than four feet from your ear (and before you say no dorm room is that small, think about sub placement from the back wall)?

This is an extreme example but just as you need to select the right mains to rooms to get proper sound, you have to do the same with subs.

And you are absolutely correct wrt wasting money.

Some people deliberately use a nearfield sub placement even in larger rooms, although I've not tried it myself. I'm not sure what you were getting at with your comment about distance from the back wall?

The only real problem I can see with a large sub in a small room is finding the space to fit it!

 

[Ultrasonic]

The core reason for using a variety of positions is that room mode excitation varies with location. Placing a sub at a null for a mode will minimally excite it, but different modes will have nulls at different locations.

The room simulator I suggested really is informative, although it only shows the amplitude response rather than the also important decay times.

 

[GrimSurfer]

Which school(s) of thought are you following here? Or if your own ideas, could you please explain your reasoning?

Lots written online about this. A reasonable article here:

https://www.audioholics.com/subwoofer-setup/subwoofer-placement-the-place-for-bass-part-1

Most rooms are symmetrical. Good practice is for the mains to be pointed down the length of the room. It is accepted practice for the mains to be spaced out from the back and side walls by at least two feet to minimize room effects. This starts to constrain sub placement, at least those involving symmetrical placement.

Do you put the subs between the mains, facing the back wall? Doing so will reinforce the null in the middle of the room.

Do you put the subs in the front corners to exploit room effects? Doing so will excite the room nodes (which is good) but won't necessarily get rid of the nulls.

When you run room mode frequencies for 80 Hz and below for average sized listening rooms, the problems of symmetry are apparent. Not in all rooms, but in most.

 

[GrimSurfer]

The core reason for using a variety of positions is that room mode excitation varies with location. Placing a sub at a null for a mode will minimally excite it, but different modes will have nulls at different locations.

The room simulator I suggested really is informative, although it only shows the amplitude response rather than the also important decay times.

Agree. Room mode calculators are very helpful in mapping out amplitude responses.

 

[GrimSurfer]

Some people deliberately use a nearfield sub placement even in larger rooms, although I've not tried it myself. I'm not sure what you were getting at with your comment about distance from the back wall?

The only real problem I can see with a large sub in a small room is finding the space to fit it!

Yeah, I've heard of people doing that. It must be devilishly difficult matching though. The trim pots on class D amps driving self-powered subs are pretty coarse.

Back and side wall distance affects reinforcement.

 

[audioBliss]

@audioBliss do you have any measured comparative distortion data for your different setups that you'd be prepared to share?

I did but all those measurements went buy, buy with my old computer. Subjectively though it just sounds so much cleaner now. I can't localize the subs as it is now whereas I have in previous setup had more of a feeling of yeah there is a subwoofer standing there. The bass is just all around me. Some frequencies are sort of more in my head which I'll remedy once I've had my go to psycoacoustic/acoustician guy here to design the room.

And with cleaner I don't just more distinct bass notes but also before it sounded like there where subwoofers playing the bass whereas now it sounds like instruments. But this part I think has a lot to do with the drivers I'm using now since I've tried using 2, 4 and now 6 of these drivers and I've compared them to Seas and Scan Speak drivers and the Ino Audio drivers just blow them out of the water in this regard even with just two of them.

I should do another measurement at higher output and measure the distortion. So then I can at least show that.

 

[audioBliss]

Ideally, a sub would have two sealed servo-controlled woofers in dipole configuration.

And as soon as I get the money for two such beasts I would try David Griesinger's placement advice for optimal (psychoacoustic) envelopment, the idea being there that bass should be perceived as if it's coming from all around instead of centered and "in the head".

This is my goal for sure! With my current setup there is more of this as suppose to having all the subs up front and having an acoustically treated room with a giant bass trap. If you have any links to his advice I'd gladly read it as I haven't ever heard of this person.